Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior an...Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior and its influencing factors are important for the long-term performance assessment of DGRs.We designed multistage mechanical(M)shear tests and thermomechanical(TM)shear tests on three 100 mm-cubic granite specimens,each containing a single inclined sawcut fracture with distinct microroughness of 8-15μm.M test results have shown that the static friction coefficient of the granite fracture decreases in proportion to the increase in the logarithm of the loading rate within the range of 1-15 kPa/s.For the given heating and boundary conditions,thermal loading rate,i.e.,thermal stress increment with heating time,is measured to be around 1 kPa/s in the fractured granite.Thermoshearing can be well predicted by the linear Mohr-Coulomb failure envelope deduced from M shear tests employing a loading rate that is comparable with the thermal loading rate.The granite fractures exhibited two distinct slip patterns during the mechanical shearing,i.e.,stick-slip observed in the smooth fracture and stable sliding in the relatively rough surface.In contrast,the mechanical loading rate(1-15 kPa/s)investigated in this study appears to not influence the slip pattern.Unlike those in M shear tests,thermoshearing in both smooth and relatively rough fractures show stable sliding with a very slow peak velocity of around 0.002μm/s.展开更多
The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure as...The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.展开更多
The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely asso...The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.展开更多
This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element...This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element method.The adhesion behavior is described based on the Maugis-Dugdale model.The adhesion-driven conjugate gradient method is employed to calculate the distribution of unknown pressures,while the discrete convolution-fast Fourier transform is utilized to compute the deformations,surface electric and magnetic potentials as well as the subsurface stresses,electric displacements,and magnetic inductions.The goal of this study is to investigate the influences of adhesion parameter,friction coefficient,coating thickness,and surface electric and magnetic charge densities on contact behaviors,such as contact area and pressures,electric and magnetic potentials,and subsurface stresses.展开更多
Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding...Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding soil.Previous studies focused on estimating the interface frictional anisotropy mobilized by snakeskin-inspired textured surfaces and sand under monotonic shear loading conditions.However,there is a need to estimate interface frictional anisotropy under repetitive shear loads.In this study,a series of repetitive direct shear(DS)tests are performed with snakeskin-inspired textured surfaces under a constant vertical stress and two shear directions(cranial first half→caudal second half or caudal first half→cranial second half).The results show that(1)mobilized shear stress increases with the number of shearing cycles,(2)cranial shearing(shearing against the scales)consistently produces a higher shear resistance and less contractive behavior than caudal shearing(shearing along the scales),and(3)a higher scale height or smaller scale length of the surface yields a higher interface friction angle across all shearing cycles.Further analysis reveals that the gap between the cranial and caudal shear zones of the interface friction angle as a function of L/H(i.e.the ratio of scale length L to scale height H)continues to decrease as the number of shearing cycles approaches asymptotic values.The directional frictional resistance(DFR)decreases as the number of shearing cycles increases.Furthermore,the discussion covers the impact of initial relative density,vertical stress,and the number of shearing cycles on interface frictional anisotropy.展开更多
Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the...Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the high mobility to ultralow resistance.However,the underlying physical mechanism of frictional weakening remains unclear.This study utilizes the discrete element method(DEM)incorporating the fragment replacement model to simulate plane shear flows under various normal stresses(0.2 e1.2 MPa)and shear velocities(0.01e2 m/s).The findings reveal a localized shear band characterized by a J-shaped velocity profile and high granular temperature,and a concentrated distribution of weak contact forces forms at a shear velocity exceeding 0.1 m/s and normal stress above 0.6 MPa.Moreover,frictional weakening is observed with increasing normal stress from 0.2 MPa to 1.2 MPa and increasing shear velocity from 0.1 m/s to 2 m/s.The evolution of the steady-state friction coefficient can be divided into two stages:an initial stage(I)and a weakening stage(II).During stage I,the steady-state friction coefficient slightly increases until reaching a peak value.However,upon entering stage II,it gradually decreases and approaches an ultimate value.The velocity-and normal stress-dependent frictional weakening can be attributed to shear localization and embedded packing structure induced by particle breakage,respectively.Finally,an optimized m(I)model is proposed to capture the full evolution of the friction coefficient with the shear strain rate,which can improve our understanding of rock avalanche dynamics.展开更多
The NiCoCrAlY coatings strengthened by three nano-particles with the same addition were prepared on a Ni-base super alloy using laser cladding technique. The dry frictional wear behaviors of the coatings at 500 ℃ in ...The NiCoCrAlY coatings strengthened by three nano-particles with the same addition were prepared on a Ni-base super alloy using laser cladding technique. The dry frictional wear behaviors of the coatings at 500 ℃ in static air were investigated. The comparison was made with the coating without nano-particles. The results show that the wear mechanism of the NiCoCrAlY coatings with nano-particles, like the coating without nano-particles, is the delamination wear due to the strong plastic deformation and oxidative wear. However, the frictional coefficient of the coatings increases and presents the decrease trend with the increase of sliding distance after adding nano-particles. Moreover, the wear rate of the coatings with nano-particles is only 34.0%-64.5% of the coating without nano-particles. Among the three nano-particles, the improvement of nano-SiC on the high temperature wear resistance of the coating is the most significant.展开更多
In order to study the relationship between pavement friction management criteria and braking distance requirements of road geometric design, an approach for determining the braking distance considering pavement fricti...In order to study the relationship between pavement friction management criteria and braking distance requirements of road geometric design, an approach for determining the braking distance considering pavement frictional properties is proposed. A finite element model （FEM） of a rolling tire under steady state is established based on theoretical hydrodynamics and mechanics principles, in which factors, including tire type, water film thickness, pavement surface properties, and vehicle speed, are considered. With the FEM, braking distances under different operating conditions are calculated. Furthermore, the allowable water film thickness is determined by comparing braking distances calculated with friction management criteria and that required by road geometric design. The results show that the braking distance is affected by the above operating conditions. As a result, it is necessary to maintain consistency between geometric design braking distance requirements and pavement friction management to achieve safe road operations.展开更多
This study investigated the micro-sliding frictional behavior of shale in fracturing fluids under varying operational conditions using Chang 7 shale oil reservoir core samples.Through systematic micro-sliding friction...This study investigated the micro-sliding frictional behavior of shale in fracturing fluids under varying operational conditions using Chang 7 shale oil reservoir core samples.Through systematic micro-sliding friction experiments,the characteristics and governing mechanisms of shale friction were elucidated.Complementary analyses were conducted to characterize the mineral composition,petrophysical properties,and micromorphology of the shale samples,providing insights into the relationship between microscopic structure and frictional response.In this paper,the characteristics and variation law of shale micro-sliding friction under different types of graphite materials as additives in LGF-80(Low-damage Guar Fluid)oil flooding recoverable fracturing fluid system were mainly studied.In addition,the finite element numerical simulation experiment of hydraulic fracturing was adopted to study the influence of the friction coefficient of natural fracture surfaces on fracture propagation and formation of the fracture network.The geometric complexity of fracture networks was systematically quantified under varying frictional coefficients of natural fracture surfaces through multi-parametric characterization and morphometric analysis.The research results show that graphite micro-particles reduce friction and drag.Based on this,this paper proposes a new idea of graphite micro-particles as an additive in the LGF-80 oil flooding recoverable fracturing fluid system to reduce friction on the fracture surface.展开更多
The stress-dilatancy relation is important for understanding fault mechanics and brittle deformation of rocks,and hence the onset of frictional instability.The principle of minimum energy ratio was proposed by Rowe,an...The stress-dilatancy relation is important for understanding fault mechanics and brittle deformation of rocks,and hence the onset of frictional instability.The principle of minimum energy ratio was proposed by Rowe,and this Rowe’s theory has been applied to deformation of granular materials.Rowe suggested that the energy ratio,which is the ratio of the energy dissipation rate to energy supply rate,would be a minimum and constant value.The relation between the rate of dilatancy and the maximum stress ratio can be extended to the case of a random assembly of irregular particles whereby the rate of internal work absorbed in frictional heat is a minimum as the mass dilates.According to Rowe’s law.展开更多
Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and coppe...Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.展开更多
The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated. A three-dimensional Navier-Stokes（N-S） equation considering viscous force and inertial force rather than Re...The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated. A three-dimensional Navier-Stokes（N-S） equation considering viscous force and inertial force rather than Reynolds equation or modified Reynolds equation is presented to model the flow field. Pressure and temperature distribution in radial and circumferential direction under three different conditions, i.e., isothermal, that considering viscosity-temperature characteristic as well as shear thinning non-Newtonian fluid are simulated, respectively, by utilizing the commercial computational fluid dynamics（CFD） software FLUENT. The results reveal that the grooves on the driven plate make the pressure, temperature distribution present periodic variation. The oil temperature and shear rate have important effects on the flow field between frictional pairs, and the oil temperature is more important parameter. The simulation results lay a theoretical foundation for the reasonable designs ofhydroviscous drive.展开更多
Some of the remarkable characteristics of natural landslides, such as surprisingly long travel distances and high velocities, have been attributed to the mechanisms of frictional heating and thermal pressurization. In...Some of the remarkable characteristics of natural landslides, such as surprisingly long travel distances and high velocities, have been attributed to the mechanisms of frictional heating and thermal pressurization. In this work, this mechanism is combined with a depth-averaged model to simulate the long runout of landslides in the condition of deformation. Some important factors that influence frictional heating and thermal pressurization within the shear zone are further considered, including velocity profile and pressurization coefficient. In order to solve the coupled equations, a combined computational method based on the finite volume method and quadratic upwind interpolation for convective kinematics scheme is proposed. Several numerical tests are performed to demonstrate the feasibility of the computational scheme, the influence of thermal pressurization on landslide run-out, and the potential of the model to simulate an actual landslide.展开更多
This paper had investigated the effects of surface wettability on the frictional resistance of turbulent horizontal flow for tap water in five pipes made of various materials and four kinds of liquids in a polytetrafl...This paper had investigated the effects of surface wettability on the frictional resistance of turbulent horizontal flow for tap water in five pipes made of various materials and four kinds of liquids in a polytetrafluoroethylene(PTFE) pipe,with the same inner diameter of 14 mm. Pressure drops were measured under different flow rates through an experimental flow loop. The contact angles and adhesion work of liquids in contact with pipe surfaces were determined using a contact angle meter. Based on the dimension and regression analyses, two kinds of modified relationships between the frictional coefficient and the surface wettability were established according to the measured results corresponding to tap water in five pipes and four liquids in PTFE pipe. The experimental results show that the surface wettability has some influence on frictional coefficient of the studied liquids flowing in macroscale pipes, and the frictional coefficient decreases with the increase of the contact angle at the same Reynolds number. Meanwhile the effect of wettability on the hydrophobic surface is greater than that on the hydrophilic one. The frictional coefficients predicted by the modified formulas have verified to be in good agreement with the experimental values, the relative errors of which are within ±6% and ±3% for the tap water flowing in five different pipes and four kinds of liquids flowing in PTFE pipe, respectively.展开更多
This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdev...This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdeveloped dynamic shear apparatus,and the effects of normal load oscillation amplitude,normal load oscillation period and sliding velocity were studied.The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process,characterized by different time spans and stress variations.Generally,a smaller oscillation amplitude,a longer oscillation period and a fast shear velocity promote the stability of the friction system,which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient.The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period(vT).Also,the rate and state friction law incorporating the parameter a that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress.Finally,the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed.This work helps us understand the sliding process and stability evolution of natural faults,and its benefits for relative hazard mitigation.展开更多
Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So f...Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.展开更多
There exist three types of nonlinear problems in large deformation processes of deep softrock engineering, i.e., nonlin- earity caused by material, geometrical and contact boundary. In this paper, the numerical method...There exist three types of nonlinear problems in large deformation processes of deep softrock engineering, i.e., nonlin- earity caused by material, geometrical and contact boundary. In this paper, the numerical method to tackle the nonlinear eontact and large deformation problem in A Software on Large Deformation Analysis for Soft Rock Engineering at Great Depth was presented. In the software, based on Lagrange multiplier method and Coulomb friction law, kinematic constraints on contact boundaries were introduced in functional function, and the finite element equations was established for two incremental large deformation analyses models, polar decomposition model and additive decomposition model. For every incremental loading step, by searching for the contact points in the potential contact interfaces （the excavation boundaries）, the Lagrange multipliers, i.e., contact forces are cal- culated iteratively by Gauss-Seidel method, and justified through satisfy the inequalities of static constraint on contact boundaries. With the software, large deformation and frictional contact of a transport roadway were analyzed numerically by the two models. The numerical examples demonstrated the efficiency of the method used in the software.展开更多
The frictional performance of gaskets is greatly affected by frictional heat in operational mine hoists. Based on frictional mechanism and heat transfer theory, the mathematical model of the temperature field of the P...The frictional performance of gaskets is greatly affected by frictional heat in operational mine hoists. Based on frictional mechanism and heat transfer theory, the mathematical model of the temperature field of the PVC gasket in an operational mine hoist was investigated, a numerical simulation using ANSYS is presented and the distribution of the temperature and heat flux were studied under basic assumptions. The results show that the temperature gradually decreases as the radius of the model increases and the isotherms are arcs of concentric semi-circle. The heat flux is of bilateral symmetry in the model and decreases radially. The theoretical values correspond with the measured values for a short time (τ≤ 100 s) when the steel wire rope slides.展开更多
The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fibe...The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as 0.01 mN and 0.03 ~m, respectively. The NbTi fibers with diameters ranging from 22.9 to 115 ~m were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remark- able stick-slip phenomenon. Notably, the fiber＇s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber＇s frictional behavior. The simulation results were consistent with the experimental data qualitatively.展开更多
The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and fri...The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and frictional properties of the brake materials were investigated.The density and open porosity of the materials as-received were about(2.1±0.1)g/cm3and(5±1)%,respectively.The brake materials were composed of 59%C,39%SiC,and 2%Si(mass fraction).The content of Si in the C/SiC brake materials modified with graphite was far less than that in the C/SiC brake materials without being modified with graphite,and the Si was dispersed.The braking curve of the 3D needled C/SiC modified with graphite was smooth,which can ensure the smooth and comfortable braking.The frictional properties under wet condition of the 3D needled C/SiC modified with graphite showed no fading.And the linear wear rate of the C/SiC modified with graphite was lower than that of the C/SiC unmodified.展开更多
基金supported by the International Collaborative Research Program(fundamental research,2021-2023)funded by Korea Institute of Civil Engineering and Building Technology(KICT).
文摘Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior and its influencing factors are important for the long-term performance assessment of DGRs.We designed multistage mechanical(M)shear tests and thermomechanical(TM)shear tests on three 100 mm-cubic granite specimens,each containing a single inclined sawcut fracture with distinct microroughness of 8-15μm.M test results have shown that the static friction coefficient of the granite fracture decreases in proportion to the increase in the logarithm of the loading rate within the range of 1-15 kPa/s.For the given heating and boundary conditions,thermal loading rate,i.e.,thermal stress increment with heating time,is measured to be around 1 kPa/s in the fractured granite.Thermoshearing can be well predicted by the linear Mohr-Coulomb failure envelope deduced from M shear tests employing a loading rate that is comparable with the thermal loading rate.The granite fractures exhibited two distinct slip patterns during the mechanical shearing,i.e.,stick-slip observed in the smooth fracture and stable sliding in the relatively rough surface.In contrast,the mechanical loading rate(1-15 kPa/s)investigated in this study appears to not influence the slip pattern.Unlike those in M shear tests,thermoshearing in both smooth and relatively rough fractures show stable sliding with a very slow peak velocity of around 0.002μm/s.
基金supported by the National Natural Science Foundation of China(Grant No.12272127)the Construction Project of Double First Class in Safety Discipline of the Universities of Henan Province(Grant No.AQ20230751).
文摘The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.
基金supported by the National Key Research and Development Project(Grant No.2023YFE0110900)the National Natural Science Foundation of China(Grant Nos.42320104003 and 42077247).
文摘The distinctive characteristics exhibited by the aftershocks of Ms6.0 induced earthquakes in Changning,Sichuan,China,have attracted significant attention.The prevalence of salt rock(halite)in this area is closely associated with induced seismic events.The present study was conducted to examine the role of halite in frictional properties.To this end,laboratory measurements were taken for simulated fault gouge composed of halite.Slide-hold-slide(SHS)shear experiments were performed on gouges with grain size<106 mm at constant normal stress from 5 MPa to 30 MPa and constant shear velocity in the range of 1-10 mm/s.Halite gouge shows higher frictional strength and frictional healing rate than most minerals.The results reveal that the fault within halite can potentially generate intense seismic events and more significant aftershocks.An increase in normal stress leads to a reduction in frictional healing,with frictional strength initially increasing and then decreasing.The elevated shear velocity following fault activation facilitates fault dilation,diminishes the frictional strength of the fault,and contributes to fault healing during the inter-seismic period.The aforementioned findings will contribute to a comprehensive understanding of the potential for the healing property of induced seismicity on faults containing halite,particularly in the Changning region of China.
基金support from the National Natural Science Foundation of China(12102085)the Postdoctoral Science Foundation of China(2023M730504)+2 种基金the Sichuan Province Regional Innovation and Cooperation Project(2024YFHZ0210)supported by the European Union-NextGenerationEU through the Italian Ministry of University and Research under the following programs:(NM)PRIN2022(Projects of Relevant National Interest)grant no.2022SJ8HTC-Electroactive Gripper for Micro-Object Manipulation(ELFIN)(NM)PRIN2022 PNRR(Projects of Relevant National Interest)grant no.P2022MAZHX-Tribological Modeling for Sustainable Design of Industrial Frictional Interfaces(TRIBOSCORE).
文摘This paper investigates the frictional adhesive contact of a rigid,electrically/magnetically conductive spherical indenter sliding past a multiferroic coating deposed onto a rigid substrate,based on the hybrid element method.The adhesion behavior is described based on the Maugis-Dugdale model.The adhesion-driven conjugate gradient method is employed to calculate the distribution of unknown pressures,while the discrete convolution-fast Fourier transform is utilized to compute the deformations,surface electric and magnetic potentials as well as the subsurface stresses,electric displacements,and magnetic inductions.The goal of this study is to investigate the influences of adhesion parameter,friction coefficient,coating thickness,and surface electric and magnetic charge densities on contact behaviors,such as contact area and pressures,electric and magnetic potentials,and subsurface stresses.
基金the funding supported from the National Research Foundation of Korea(NRF)grant funded by the Korea Government MSIT(No.2021R1C1C1006003).
文摘Understanding frictional anisotropy,which refers to the variation in frictional resistance based on the shear direction,is crucial for optimizing the friction angle between a bio-inspired structure and the surrounding soil.Previous studies focused on estimating the interface frictional anisotropy mobilized by snakeskin-inspired textured surfaces and sand under monotonic shear loading conditions.However,there is a need to estimate interface frictional anisotropy under repetitive shear loads.In this study,a series of repetitive direct shear(DS)tests are performed with snakeskin-inspired textured surfaces under a constant vertical stress and two shear directions(cranial first half→caudal second half or caudal first half→cranial second half).The results show that(1)mobilized shear stress increases with the number of shearing cycles,(2)cranial shearing(shearing against the scales)consistently produces a higher shear resistance and less contractive behavior than caudal shearing(shearing along the scales),and(3)a higher scale height or smaller scale length of the surface yields a higher interface friction angle across all shearing cycles.Further analysis reveals that the gap between the cranial and caudal shear zones of the interface friction angle as a function of L/H(i.e.the ratio of scale length L to scale height H)continues to decrease as the number of shearing cycles approaches asymptotic values.The directional frictional resistance(DFR)decreases as the number of shearing cycles increases.Furthermore,the discussion covers the impact of initial relative density,vertical stress,and the number of shearing cycles on interface frictional anisotropy.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFC3008300 and 2023YFC3008302)the National Natural Science Foundation of China(Grant No.U22A20603).
文摘Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the high mobility to ultralow resistance.However,the underlying physical mechanism of frictional weakening remains unclear.This study utilizes the discrete element method(DEM)incorporating the fragment replacement model to simulate plane shear flows under various normal stresses(0.2 e1.2 MPa)and shear velocities(0.01e2 m/s).The findings reveal a localized shear band characterized by a J-shaped velocity profile and high granular temperature,and a concentrated distribution of weak contact forces forms at a shear velocity exceeding 0.1 m/s and normal stress above 0.6 MPa.Moreover,frictional weakening is observed with increasing normal stress from 0.2 MPa to 1.2 MPa and increasing shear velocity from 0.1 m/s to 2 m/s.The evolution of the steady-state friction coefficient can be divided into two stages:an initial stage(I)and a weakening stage(II).During stage I,the steady-state friction coefficient slightly increases until reaching a peak value.However,upon entering stage II,it gradually decreases and approaches an ultimate value.The velocity-and normal stress-dependent frictional weakening can be attributed to shear localization and embedded packing structure induced by particle breakage,respectively.Finally,an optimized m(I)model is proposed to capture the full evolution of the friction coefficient with the shear strain rate,which can improve our understanding of rock avalanche dynamics.
基金Project(20060287019)supported by the Research Fund for Doctoral Program of Higher Education of ChinaProject(kjsmcx07001)supported by the Opening Research Fund of Jiangsu Key Laboratory of Tribology,ChinaProject(BK2010267)supported by the Jiangsu Provincial Natural Science Foundation of Jiangsu Province,China
文摘The NiCoCrAlY coatings strengthened by three nano-particles with the same addition were prepared on a Ni-base super alloy using laser cladding technique. The dry frictional wear behaviors of the coatings at 500 ℃ in static air were investigated. The comparison was made with the coating without nano-particles. The results show that the wear mechanism of the NiCoCrAlY coatings with nano-particles, like the coating without nano-particles, is the delamination wear due to the strong plastic deformation and oxidative wear. However, the frictional coefficient of the coatings increases and presents the decrease trend with the increase of sliding distance after adding nano-particles. Moreover, the wear rate of the coatings with nano-particles is only 34.0%-64.5% of the coating without nano-particles. Among the three nano-particles, the improvement of nano-SiC on the high temperature wear resistance of the coating is the most significant.
基金The Research and Innovation Foundation for Graduate Students in Jiangsu Province(No.CX10B_070Z)
文摘In order to study the relationship between pavement friction management criteria and braking distance requirements of road geometric design, an approach for determining the braking distance considering pavement frictional properties is proposed. A finite element model （FEM） of a rolling tire under steady state is established based on theoretical hydrodynamics and mechanics principles, in which factors, including tire type, water film thickness, pavement surface properties, and vehicle speed, are considered. With the FEM, braking distances under different operating conditions are calculated. Furthermore, the allowable water film thickness is determined by comparing braking distances calculated with friction management criteria and that required by road geometric design. The results show that the braking distance is affected by the above operating conditions. As a result, it is necessary to maintain consistency between geometric design braking distance requirements and pavement friction management to achieve safe road operations.
文摘This study investigated the micro-sliding frictional behavior of shale in fracturing fluids under varying operational conditions using Chang 7 shale oil reservoir core samples.Through systematic micro-sliding friction experiments,the characteristics and governing mechanisms of shale friction were elucidated.Complementary analyses were conducted to characterize the mineral composition,petrophysical properties,and micromorphology of the shale samples,providing insights into the relationship between microscopic structure and frictional response.In this paper,the characteristics and variation law of shale micro-sliding friction under different types of graphite materials as additives in LGF-80(Low-damage Guar Fluid)oil flooding recoverable fracturing fluid system were mainly studied.In addition,the finite element numerical simulation experiment of hydraulic fracturing was adopted to study the influence of the friction coefficient of natural fracture surfaces on fracture propagation and formation of the fracture network.The geometric complexity of fracture networks was systematically quantified under varying frictional coefficients of natural fracture surfaces through multi-parametric characterization and morphometric analysis.The research results show that graphite micro-particles reduce friction and drag.Based on this,this paper proposes a new idea of graphite micro-particles as an additive in the LGF-80 oil flooding recoverable fracturing fluid system to reduce friction on the fracture surface.
基金funded by a Grantin-Air for Scientific Research(24244077).
文摘The stress-dilatancy relation is important for understanding fault mechanics and brittle deformation of rocks,and hence the onset of frictional instability.The principle of minimum energy ratio was proposed by Rowe,and this Rowe’s theory has been applied to deformation of granular materials.Rowe suggested that the energy ratio,which is the ratio of the energy dissipation rate to energy supply rate,would be a minimum and constant value.The relation between the rate of dilatancy and the maximum stress ratio can be extended to the case of a random assembly of irregular particles whereby the rate of internal work absorbed in frictional heat is a minimum as the mass dilates.According to Rowe’s law.
基金National Natural Science Foundation of China (50432020)Henan Innovation Project for University Prominent Re- search Talents (2007KYCX008)+3 种基金Henan Education Department Science and Technology Project (2007430004)Henan Plan Project for College Youth Backbone TeacherHenan University of Science and Technology Major Pre-research Foundation (2005ZD003)Henan University of Science and Technology Personnel Scientific Research Foundation (of023)
文摘Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.
基金National Natural Science Foundation of China(No.50475106)
文摘The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated. A three-dimensional Navier-Stokes（N-S） equation considering viscous force and inertial force rather than Reynolds equation or modified Reynolds equation is presented to model the flow field. Pressure and temperature distribution in radial and circumferential direction under three different conditions, i.e., isothermal, that considering viscosity-temperature characteristic as well as shear thinning non-Newtonian fluid are simulated, respectively, by utilizing the commercial computational fluid dynamics（CFD） software FLUENT. The results reveal that the grooves on the driven plate make the pressure, temperature distribution present periodic variation. The oil temperature and shear rate have important effects on the flow field between frictional pairs, and the oil temperature is more important parameter. The simulation results lay a theoretical foundation for the reasonable designs ofhydroviscous drive.
基金supported by the National Natural Science Foundation of China (Grant No. 41790433)NSFC-ICIMOD (Grant No. 41661144041)+1 种基金Key Research and Development Projects of Sichuan Province (2017SZ0041)CAS "Light of West China" Program
文摘Some of the remarkable characteristics of natural landslides, such as surprisingly long travel distances and high velocities, have been attributed to the mechanisms of frictional heating and thermal pressurization. In this work, this mechanism is combined with a depth-averaged model to simulate the long runout of landslides in the condition of deformation. Some important factors that influence frictional heating and thermal pressurization within the shear zone are further considered, including velocity profile and pressurization coefficient. In order to solve the coupled equations, a combined computational method based on the finite volume method and quadratic upwind interpolation for convective kinematics scheme is proposed. Several numerical tests are performed to demonstrate the feasibility of the computational scheme, the influence of thermal pressurization on landslide run-out, and the potential of the model to simulate an actual landslide.
基金supported by the National Major Science&Technology Project of China(No.2016ZX05025004-005)the Science&Technology Project of Sichuan Province(Grant No.2015JY0099)
文摘This paper had investigated the effects of surface wettability on the frictional resistance of turbulent horizontal flow for tap water in five pipes made of various materials and four kinds of liquids in a polytetrafluoroethylene(PTFE) pipe,with the same inner diameter of 14 mm. Pressure drops were measured under different flow rates through an experimental flow loop. The contact angles and adhesion work of liquids in contact with pipe surfaces were determined using a contact angle meter. Based on the dimension and regression analyses, two kinds of modified relationships between the frictional coefficient and the surface wettability were established according to the measured results corresponding to tap water in five pipes and four liquids in PTFE pipe. The experimental results show that the surface wettability has some influence on frictional coefficient of the studied liquids flowing in macroscale pipes, and the frictional coefficient decreases with the increase of the contact angle at the same Reynolds number. Meanwhile the effect of wettability on the hydrophobic surface is greater than that on the hydrophilic one. The frictional coefficients predicted by the modified formulas have verified to be in good agreement with the experimental values, the relative errors of which are within ±6% and ±3% for the tap water flowing in five different pipes and four kinds of liquids flowing in PTFE pipe, respectively.
基金the National Natural Science Foundation of China(Nos.51904359,51978677 and 52111530089)the Guangdong Provincial Department of Science and Technology(No.2019ZT08G090)+2 种基金the Enhanced National Key Basic Research Program(No.2019-JCJQ-ZD-352-00-04)the Science and Technology Program for Sustainable Development of Shenzhen(No.KCXFZ202002011008532)the Open Research Fund of the State Key Laboratory of Coal Resources and Safe Mining,CUMT(No.SKLCRSM20KF002).
文摘This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress.A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a selfdeveloped dynamic shear apparatus,and the effects of normal load oscillation amplitude,normal load oscillation period and sliding velocity were studied.The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process,characterized by different time spans and stress variations.Generally,a smaller oscillation amplitude,a longer oscillation period and a fast shear velocity promote the stability of the friction system,which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient.The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period(vT).Also,the rate and state friction law incorporating the parameter a that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress.Finally,the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed.This work helps us understand the sliding process and stability evolution of natural faults,and its benefits for relative hazard mitigation.
基金supported by the National Natural Science Foundation of China(No.51772020)Beijing Natural Science Foundation(No.2182058)+1 种基金Beijing Government Funds for the Constructive Project of Central UniversitiesEquipment Development Department of the National Military Commission Foundation of China(No.JZX7Y20190262063601)。
文摘Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.
基金subsidized by special funds for the National Basic Research Program of China (No.2002cb412708)supported by the Opening Funds of the State Key Laboratory of Hydroscience and Engineering of China (No.sklhse-2007-D-02)
文摘There exist three types of nonlinear problems in large deformation processes of deep softrock engineering, i.e., nonlin- earity caused by material, geometrical and contact boundary. In this paper, the numerical method to tackle the nonlinear eontact and large deformation problem in A Software on Large Deformation Analysis for Soft Rock Engineering at Great Depth was presented. In the software, based on Lagrange multiplier method and Coulomb friction law, kinematic constraints on contact boundaries were introduced in functional function, and the finite element equations was established for two incremental large deformation analyses models, polar decomposition model and additive decomposition model. For every incremental loading step, by searching for the contact points in the potential contact interfaces （the excavation boundaries）, the Lagrange multipliers, i.e., contact forces are cal- culated iteratively by Gauss-Seidel method, and justified through satisfy the inequalities of static constraint on contact boundaries. With the software, large deformation and frictional contact of a transport roadway were analyzed numerically by the two models. The numerical examples demonstrated the efficiency of the method used in the software.
基金Projects 50225519 supported by the National Outstanding Youth Science Foundation of China0E4458 by the Youth Science Foundation of China Univer-sity of Mining and Technology
文摘The frictional performance of gaskets is greatly affected by frictional heat in operational mine hoists. Based on frictional mechanism and heat transfer theory, the mathematical model of the temperature field of the PVC gasket in an operational mine hoist was investigated, a numerical simulation using ANSYS is presented and the distribution of the temperature and heat flux were studied under basic assumptions. The results show that the temperature gradually decreases as the radius of the model increases and the isotherms are arcs of concentric semi-circle. The heat flux is of bilateral symmetry in the model and decreases radially. The theoretical values correspond with the measured values for a short time (τ≤ 100 s) when the steel wire rope slides.
基金This work is supported by the National Natural Science Foundation of China （No. 11622217）
文摘The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as 0.01 mN and 0.03 ~m, respectively. The NbTi fibers with diameters ranging from 22.9 to 115 ~m were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remark- able stick-slip phenomenon. Notably, the fiber＇s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber＇s frictional behavior. The simulation results were consistent with the experimental data qualitatively.
基金Project(46-QP-2009)supported by the Research Fund of State Key Laboratory of Solidification Processing(NWPU),ChinaProject supported by the Program for Changjiang Scholars and Innovative Research Team in Chinese University
文摘The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration,slurry infiltration and liquid silicon infiltration process.The microstructure and frictional properties of the brake materials were investigated.The density and open porosity of the materials as-received were about(2.1±0.1)g/cm3and(5±1)%,respectively.The brake materials were composed of 59%C,39%SiC,and 2%Si(mass fraction).The content of Si in the C/SiC brake materials modified with graphite was far less than that in the C/SiC brake materials without being modified with graphite,and the Si was dispersed.The braking curve of the 3D needled C/SiC modified with graphite was smooth,which can ensure the smooth and comfortable braking.The frictional properties under wet condition of the 3D needled C/SiC modified with graphite showed no fading.And the linear wear rate of the C/SiC modified with graphite was lower than that of the C/SiC unmodified.
